Structures and electrochemistry of monomeric and dimeric CpCo(dithiolene) complexes with substituted benzene-1,2-dithiolate ligand

The molecular structures of [CpCo(tdt)] and [CpCo(Cl3bdt)] were determined by X-ray diffraction studies. [CpCo(tdt)] was monomeric in the crystal, coordinatively unsaturated with 16-electrons and had a two-legged piano-stool geometry. [CpCo(Cl3bdt)] was dimeric, coordinatively saturated with 18-electrons and became a three-legged piano-stool geometry. There were two crystallographically independent molecules in [CpCo(tdt)] and both molecules were associated with intermolecular Cp⋯Cp face-to-face interaction. Some intermolecular Co⋯S interactions were also observed between the crystallographically identical molecules of [CpCo(tdt)]. The cyclic voltammograms of [CpCo(tdt)] and [CpCo(Cl2bdt)] exhibited single oxidation waves, but those of [CpCo(Cl3bdt)] and [CpCo(Cl4bdt)] showed two oxidation waves due to both the monomer and dimer in the solutions. Electrochemical oxidations of these monomers occurred dimerizations by EC reactions in the solutions, and the oxidized dimers could be rereduced to form the original monomers by EC reactions. Spectroelectrochemical data using OTTLE supported the reversible ECEC reactions. Abbreviations of dithiolene ligands are as follows: tdt = toluene-3,4-dithiolate, Cl2bdt = 3,6-dichlorobenzene-1,2-dithiolate, Cl3bdt = 3,4,6-trichlorobenzene-1,2-dithiolate, and Cl4bdt = tetrachlorobenzene-1,2-dithiolate.